FR2716107A1 - Femoral shaft implant for hip joint replacement prosthesis - Google Patents

Abstract

The femoral shaft of the implant includes a neck portion (3) with a frustoconical head (4) oriented at an angle relative to the vertical portion (2) of the shaft body. The vertical portion has an upper section (12) whose transverse cross-section decreases progressively towards its lower end, and a lower section (6) of cylindrical or approximately cylindrical shape. The upper section of the shaft has a roughened surface and includes eight or nine grooves (17) parallel to the longitudinal axis of the shaft, while the lower section of the shaft is polished. The angle (alpha) between the neck and the vertical portion is between 130 and 140 degrees, and the neck includes a central section with a flat lateral area (19) on each face.

Description

FEMALE IMPLANT FOR HIP PROSTHESIS
The present invention relates to a femoral implant for hip prosthesis, of the type comprising a femoral stem intended to be introduced into the femur of a patient and a neck oriented angularly relative to the stem, said neck being provided with a part of frustoconical end on which is fitted a ball-shaped head capable of co-operating with friction with an acetabulum of iliac bone.

 It finds a particularly important although not exclusive application in the field of orthopedic surgery.

 We already know (FR-A-2,629,707) femoral implants for hip prosthesis of the type described above.

 These implants have drawbacks.

 Indeed, they do not always make it possible to avoid loosening of the rod relative to the femur, leading to relative movements which can be painful for the patient. They are also not easy to set up by an operator.

Finally, they generate additional mechanical stresses on the bone, once the prosthesis is in place, the distance between the center of the ball-shaped head and the top of the rod varying according to the recommended implants.

 Implants are also known (FR-A-2,666,984), the stem of which is provided with grooves suitable for promoting anchoring in the femur.

 Here again, however, such rods have the disadvantage of being difficult to install, and then, if necessary, difficult to remove.

 The present invention aims to provide a femoral implant that better meets those previously known to the requirements of practice, in particular in that it provides a rod allowing better filling of the medullary canal of the femur, in that it allows to restore the natural configuration. of the joint whatever the size of the prosthesis and the morphology of the patient, in that it offers a greater anchoring surface in the metaphyseal region, and this without this configuration preventing any subsequent extraction for replacement of the femoral implant, while opposing the insertion, and in that it facilitates the orientation of the prosthesis during its introduction, then the reduction thereof in the joint.

 For this purpose, the invention essentially provides a femoral implant for hip prosthesis, comprising a femoral stem intended to be introduced into the femur of a patient and a neck oriented angularly with respect to the stem, said neck being provided with a frustoconical end part on which is fitted a ball-shaped head suitable for frictionally cooperating with an acetabulum of iliac bone, characterized in that the rod has an upper part of decreasing cross section from top to bottom of ellipsoid shape and a lower part of cylindrical or substantially cylindrical cross section.

 In advantageous embodiments, one or more of the following arrangements is used - The angle formed by the neck with the rod is between about 130 and about 140.

- The collar has a middle part provided on each side with a lateral flat.

 Such an arrangement allows the articular amplitude to be increased - the upper part of the rod is treated by shot blasting and has grooves parallel to the rod, of decreasing depth from top to bottom.

 Such an arrangement makes it possible to increase the anchoring surface by opposing a sinking of the rod into the femur while subsequently allowing its easy extraction, if necessary - the part of the neck serving as a junction with the rod has an upper face perpendicular to the rod, provided with a substantially rectangular slot-shaped recess comprising a conical median cavity having a diameter at the base of greater dimension than the width of the slot.

 Such an arrangement makes it possible to orient the prosthesis using a tool in the form of a screwdriver, during its introduction into the femur. The rotation of the rod in the medullary cavity is moreover facilitated by the rounded edges of the rod of ellipsoidal or circular section and its polished lower part.

 Once the implant is in place and oriented, the reduction of the prosthesis in the joint is then carried out using a tool whose end is in the shape of a needle, which allows the pivoting of the body while allowing strong compression. down the stem.

 The invention also provides equipment for producing a hip prosthesis, comprising a series of femoral implants, characterized in that the distances between the median axes of the rods and the centers of the balls fitted on the frustoconical ends of the corresponding necks are substantially constant whatever the lengths and the transverse dimensions of the rods of the implants.

 Advantageously, the equipment further comprises a set of rapes and a set of removable test collars of variable length suitable for being fixed on the upper parts of the rapes.

 In another advantageous embodiment, the equipment is such that for each implant rod there is a slightly larger cross section dimension.

 Such an arrangement minimizes the risk of fractures of the femur during the sealing of the stem in the medullary cavity.

 The invention will be better understood on reading the following description of an embodiment given by way of nonlimiting example.

 It refers to the accompanying drawings in which - Figure 1 is a side elevational view of a femoral implant according to an embodiment of the invention.

- Figures 2a to 2e give the cross sections of the rod respectively along lia - lia; IIb - IIb; lic - lic; IId - IId and
IIe - IIe of Figure 1.

- Figures 3a and 3b show the half cross sections, in larger dimension, of the rod, in two different cutting locations (IIIa - IIIa and IIIb - IIIb).

- Figure 4 is a front elevation view of the stem of the implant of Figure 1.

- Figures 5a and 5b show respectively in top view, and in section along Vb-Vb of Figure 5a, on a larger scale, the recess of the upper face of the rod allowing easy introduction and reduction of the implant.

 FIG. 1 shows a femoral implant 1 for a titanium hip prosthesis, comprising a femoral stem 2 forged or machined in the mass, intended to be introduced into the femur of a patient, and a neck 3, oriented angularly with respect to the rod with an angle a of 135 ", and formed in one piece with said rod.

 The neck is provided with an upper end portion 4 of frustoconical shape, of weak conicity of the Morse cone type, on which is fitted a head 5 in the form of a spherical ceramic ball capable of cooperating with friction with a bone cup iliac or acetabular implant.

The stem has an increasing cross section from bottom to top (see Figures 11a to
IIe).

 More specifically, the rod 2 is substantially cylindrical over the first third 6 of its height, with a smooth or polished surface, in the lower part (Figures 2a and 2b).

 From the end of the first third of its height, the section gradually takes an ellipsoid shape which is more and more deformed towards the internal part of the angle a.

 The rod therefore has a section comprising an outer half 7 substantially in the form of a semicircle, with a center passing through the axis 10 of the rod and of radius increasing from the bottom to the top, and a half 8, internal to the 'angle a, more and more oblong.

 In the upper part of the rod, at level 9 at the start of the junction with the neck 3 (see FIG. 2e), the distance d between the center 10 of the semicircle 7 and the distal end of the oblong part 8, is substantially the triple the radius r of the semicircle 7.

 The upper part of the rod 12, that is to say the part substantially situated above two-fifths of the height h of the said rod, is treated by shot blasting, which gives it a graphite appearance, with a surface of very fine particle size. .

 The stem has three-quarters of its height, a convex shoulder 13, directed towards the neck, ending in 14 by a beak of intersection with the axis 10.

 The plane of intersection 15 between the neck 3 and the rod 2 is perpendicular to the axis 16 of the neck coaxial with the axis of the frustoconical end 4, the axes 16 and 10 therefore forming the angle a which has been defined above.

 The rod 2 furthermore comprises in the upper part 12, vertical grooves 17, parallel to the axis 10 of the rod, for example from half the height of the rod. The grooves 17 are of decreasing depth from top to bottom, as appears more precisely in view of the half-sections of Figures 3a and 3b.

 The grooves are of decreasing length from bottom to top, their lower end being part of a curve substantially parallel to the internal curve of the rod on the side of the angle a, and their upper end being delimited by the plane of intersection. 15.

 The number of grooves is between three and ten, for example equal to eight.

 More specifically, the depth of the grooves increases from the bottom up, between a substantially zero depth, and a depth of the order of one to two millimeters for the longest grooves.

 The neck 3 has a middle portion 18 provided, on each lateral side, with a flat 19, and having an upper face 20 perpendicular to the axis 10 of the rod, provided with a recess 21 which will now be described with reference in Figures 5a and 5b.

 The recess 21 has a substantially parallelepipedal slit 22, with a depth for example of between around 3 mm and around 1 cm. The slot has, in section (see FIG. 5b), a bowl shape comprising a curved bottom, the radius of which is around 10 cm.

 The recess further comprises a central cavity 23, substantially conical or frustoconical, with a rounded top 24 directed towards the bottom of the rod.

 The diameter of the cavity 23, the axis 25 of which passes through the center of the slot 22, is larger than the width of said slot 22, for example double.

 As is obvious and as follows from the above, the present invention is not limited to the embodiment more particularly described here. On the contrary, it embraces all the variants falling within the framework of equivalences.

Claims (10)

 1. Femoral implant (1) for hip prosthesis, comprising a femoral stem (2) intended to be introduced into the femur of a patient and a neck (3) oriented angularly relative to the stem, said neck being provided with a frustoconical end part (4) on which is fitted a ball-shaped head (5) capable of co-operating with friction with an acetabulum of the iliac bone, characterized in that the rod (2) has an upper part (12 ) of decreasing cross section from top to bottom of ellipsoid shape and a lower part (6) of cylindrical or substantially cylindrical cross section.  2. femoral implant according to claim 1, characterized in that the angle a formed by the neck (3) with the rod (2) is between about 130 and about 140.  3. Femoral implant according to any one of the preceding claims, characterized in that the neck (3) has a middle part (18) provided on each side with a lateral flat (19).  4. femoral implant according to any one of the preceding claims, characterized in that the upper part (12) of the rod is treated by shot blasting and has grooves (17) parallel to the rod, of decreasing depth from top to bottom .  5. Femoral implant according to claim 4, characterized in that the rod (2) has 8 or 9 grooves.  6. Femoral implant according to any one of the preceding claims, characterized in that the lower part (6) is polished.  7. femoral implant according to any one of the preceding claims, characterized in that the part of the neck serving as a junction with the rod has an upper face (20) perpendicular to the rod, provided with a recess (21) in the form of substantially rectangular slot comprising a conical median cavity (23) having a diameter at the base of greater dimension than the width of the slot.  8. Equipment for producing a hip prosthesis, comprising a series of femoral implants according to any one of the preceding claims, characterized in that the distances between the median axes of the rods and the centers of the balls fitted on the ends frustoconical of the corresponding necks are substantially constant whatever the lengths and the transverse dimensions of the rods of said implants.  9. Equipment according to claim 8, characterized in that it further comprises a set of rapes and a set of removable test collars of variable length suitable for being fixed on the upper parts of said rapes.  10. Equipment according to claim 9, characterized in that for each implant rod there is a rape of slightly larger transverse dimensions.